Characterizing the Water-Forming Reaction on Graphite- and Ceria-Supported Palladium Nanoparticles and Nanoislands by the Work Function

Abstract

The water-forming reaction (WFR) between oxygen and hydrogen on metal surfaces is an important reaction in heterogeneous catalysis. Related research mostly focused on crystalline metal surfaces and thick films; however, supported nanoparticles (NP) have been rarely considered as well as a possible influence of the support on the NP catalytic activity. Here, we report on the WFR on graphite-supported palladium NPs and nanoislands (NI), which are characterized at room temperature and under ultrahigh vacuum conditions (UHV) by scanning tunneling microscopy (STM), noncontact atomic force microscopy (nc-AFM), Kelvin probe force microscopy (KPFM), and X-ray photoemission spectroscopy (XPS). We show that during the first cycles of sequential O2 and H2 pulses, atomic H reacts off preadsorbed atomic O, which can be followed by KPFM via monitoring the change in work function (WF) at the NPs and NIs. However, after a few WFR cycles, the WF changes get smaller and the mean WF of the Pd increases due to an irreversible deactivation of the catalyst: a filament structure is formed on the facets by O and C, which the latter probably gets released from the graphite during the WFR. In strong contrast to the Pd/graphite catalyst, the WFR can be followed without any changes during an unlimited number of cycles on a carbon-free Pd/cerium oxide/Cu(111) catalyst, which clearly shows that the support plays a role in the WFR on nanometer-sized Pd catalysts.

Influence of Surface Roughness on the Work Function of Gold: A Density Functional Theory Study

“…The work function (WF), a fundamental property of materials, is widely used to describe various surface chemical processes, including corrosion, friction, oxidation, and the attachment of molecules. ,− While limited studies have investigated the relationship between surface roughness and the gold work function, research on other metals has demonstrated the impact of surface roughness on the work function. Notably, metals like silver, , copper, and indium tin oxide (ITO) show a decrease in work function as surface roughness increases, whereas aluminum and magnesium − exhibit the opposite trend.…”